A wide variety of colorants have been approved by the FDA for use in foods, pharmaceuticals, and cosmetic preparations. Extensive toxicity studies have been performed on each of these compounds, and they have been found to be nontoxic. However, relatively little research has been performed to determine whether use of these colorants in foods, drugs, and cosmetics is actually beneficial, rather than simply not harmful.
We have been conducting studies designed to help fill this gap. Our research is directed towards use of natural and synthetic food colorants in the inhibition of carcinogenesis. In past work, we have described inhibition of tumor formation by natural colorants and extracts of fruits, vegetables, and other plant parts (Kapadia et al., Proc. Int Congress on Nat. Prod. Research, Abstract No. 225; Halifax, Canada; 1994). Extracts of turmeric, paprika, and annatto seeds have been found to be of great interest, particularly in the prevention of cancer. Paprika extracts, obtained from Capsicum annum L. (Fam: Solanacaea), are among the oldest and most important carotenoid extracts. The main carotenoids present in paprika are capsanthin (I) and capsorubin (II), largely as their acyl esters. Other minor components are present. ##STR1## Annatto seeds are the seeds of the tropical bush Bixa orellana L. (Family: Bixaceae). The major pigment is the carotenoid cis-bixin (III), the monomethyl ester of diapocarotenoic acid (IV; also known as cis-norbixin). Trans-bixin and cis-norbixin are also present as minor constituents. Trans-bixin and cis-bixin are both sparingly water-soluble, and may be converted to a water-soluble salt of the corresponding norbixin upon alkali hydrolysis. ##STR2## Turmeric, also called curcuma, is a fluorescent yellow-colored extract from the rhizomes of several species of the curcuma plant. Curcuma longa is the usual commercial source. The pigments curcumin (V), demethoxycurcumin (VI), and bisdemethoxycurcumin (VII) occur in every species, together with minor ingredients that contribute to the flavor. ##STR3## Other natural colorants that have been found to be of interest include the betanins and the anthocyanins. Betanins may be readily extracted from beet roots, and anthocyanins may be extracted from grapes, red onion skin, cranberries, and other plant-derived materials.
The studies reported herein include in vitro studies of inhibition of Epstein-Barr virus early antigen (EBV-EA) induction studies by synthetic colorants and by natural plant extracts and colorants. The Epstein-Barr virus (EBV)is a member of the herpes virus family, and has been implicated in the pathogenesis of Burkitt's lymphoma, nasopharyngeal carcinoma, and B lymphocyte neoplasms. Infection of a human by EBV is commonly followed by a latency period, when the virus is present intracellularly in an unexpressed state. T cell suppressor mechanisms of the immune response to EBV are effective in the inhibition of acute EBV infection. If these mechanisms fail, Burkitt's lymphoma, nasopharyngeal carcinoma, and B cell lymphomas may emerge. This is a serious problem during the postoperative recuperation period following organ transplants, as immunosuppresive therapy is often used to prevent rejection. It is therefore important to find new cancer chemopreventive agents which prevent formation of tumors linked to the Epstein-Barr virus. In vitro inhibition of EBV-EA induction in Epstein-Barr virus genome-carrying cells by a potential cancer chemopreventive compound serves as an excellent sign that the compound may inhibit tumor formation in a living organism. In fact, inhibitory activity toward EBV-EA induction is often taken as a measure of anti-tumor promoting activity.
In vivo studies of inhibition of skin tumor formation by synthetic and natural colorants were also performed, using a two-stage mouse skin carcinogenesis test. A diagram illustrating such a test is provided in FIG. 1. Two mice (or groups of mice) are each treated with a compound known to initiate tumor formation (stage 1). In FIG. 1, 7,12-dimethylbenza!anthracene (DMBA) is used as the tumor initiator; other compounds may be used. The mice are then subjected to a condition or compound on a continued basis that promotes tumor formation (stage 2). Ultraviolet B radiation serves as an effective tumor promoter, as shown in FIG. 1. Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) also serves as a promoter of skin tumors. One animal, the test animal, is provided an inhibitor of tumor promotion. The inhibitor may be provided in drinking water or topically applied to the skin. The other animal, the control animal, is provided with no inhibitor. At the end of a defined period, the number of tumors on the test animal is compared to the number of tumors on the control animal. Similar tests were performed for inhibition of pulmonary tumor formation, using injected 4-nitroquinoline 1-oxide as a tumor initiator and glycerol, provided in drinking water as a tumor promotor.